Caption: Geothermal power. Steam-carrying pipes and a cooling tower at the Wairakei geothermal electricity generation plant. Geothermal power stations are only commercially viable in areas where the Earth's crust is thin, allowing our planet's internal heat to reach the surface at a fast rate. The pipes of the Wairakei power station can carry steam at a speed of 200 kilometres per hour at a pressure of 3.5 atmospheres. The station can generate 153 megawatts of electricity. Photographed on North Island, New Zealand.